The present invention relates to pipe couplings for connecting together two plain-ended pipes in a fluid-tight manner, of the type consisting of a tubular casing formed with a longitudinal gap, a sealing gasket of resilient flexible material typically of rubber or synthetic rubber, arranged within the casing, and tensioning means for reducing the width of the longitudinal gap so as to tighten the casing around the gasket. In use, the sealing sleeve is placed around the adjacent pipe ends and the tensioning means are tightened to clamp the sleeve against the outer surfaces of the pipe ends to form a fluid tight seal.
One known pipe coupling of this type is described in our patent specification EP-A-0542779.
Joining together pipes with plain ends with such couplings avoids the need for pipe preparation and is therefore quicker and more economical than other methods such as welding, screw threading, flanging, grooving or shouldering.
In the coupling of the above-mentioned patent specification, the sealing gasket has circumferential slots and a gripping ring with inwardly projecting gripping teeth in each slot. In use when the tensioning means are tightened around the casing the gripping teeth penetrate the sealing gasket at the bottom of the slot and engage the outer surface of the pipe to hold the pipe ends against axial displacement.
Couplings of the type described above are often required for use in systems where resistance to fire is required. For such applications the coupling may have to pass a specific fire test. Fire tests often require the coupling to perform when subjected to a flame temperature of, typically 800xc2x0 C. and under a variety of simulated pipeline conditions. The test conditions depend on the testing authority and/or the intended field of application. For some tests the pipes will be empty, for others they will be pressurized with cold water or with hot water at, typically, 80xc2x0 C. After the test, which is typically of 30 minutes duration, the coupling will usually be expected to withstand a pressure test to the published maximum test pressurexe2x80x94typically 24 bars.
The known pipe couplings cope extremely well with most of these test by virtue of the fact that within the time span of the test, the rubber gaskets do not exceed the temperature performance limitations whereby the rubber will melt, revert or decompose and thus lose its sealing ability. In general, provided the gasket remains below, say 250xc2x0 C., for the duration of the test, it will not fail.
There are some fire tests, particularly for sprinkler systems, where the pipes must be empty for the duration of the test and thus the rubber is not cooled by the internal pipe medium. Recently introduced new higher marine standards have meant that the coupling has to withstand flames of greater intensity or temperature than was previously required. This is generally reflective of a raising of standards in the shipping industry.
There is a requirement for a pipe coupling that can meet the higher fire performance requirements whilst retaining the advantages of the known gasketed mechanical coupling of time saving in installation, flexibility and ease of installation. One possibility is to wrap the coupling, after installation, with mineral wool and fire-shielding fabrics in order to reduce the temperature within the coupling to less than the critical value of approximately 250xc2x0 C. There are, however, severe drawbacks with this approach. The materials needed are extremely expensive; they have to be expertly prepared to a given formula ensuring a certain number of wraps and an exact thickness of material, to ensure the desired degree of protection; each size of coupling will require a different length of material, and in many cases materials will have to be pre-prepared to fit round the coupling rather than being cut in situ. Consequently, this solution is feasible but impractical.
According to the present invention a pipe coupling for coupling together two pipes in a fluid-tight manner comprises a tubular casing, a tubular sealing gasket located within the casing, and means for tensioning the is casing around the gasket, the casing comprising an inner tubular casing and an outer tubular casing, a layer of fire-resistant thermally-insulating material being disposed between the inner and outer casings.
The coupling of the invention combines the advantages of the fire-shielding materials with a pipe coupling such that the coupling maybe supplied complete with its own fire shield and be fitted in place without any further preparation. By placing a fire sleeve of, typically 3 mm-5 mm thickness between the inner and outer casing of the coupling such that when the coupling is tightened it will slide easily over the fire shield without rucking and close down around the pipe, a satisfactory fire performance can be achieved without affecting its other properties of sealing or anchoring the pipes.
The problems which have been solved in enabling this invention to work have been to reconcile the tolerance of the coupling to having an extra 6-10 mm of diameter between the pipe surface and the outer casing of the coupling, to ensure that the fire shield does not ruck when the coupling is closed, and to ensure that the coupling is protected fully about its entire circumference at all times.
The difference over previous couplings is so great that a coupling in accordance with the present invention has been constructed which can withstand temperatures of 950xc2x0 C. without any deterioration. In unprotected couplings failure would occur under these conditions in less than 6 minutes.